Clinical Technique for Locating Macular Scotoma

1
Clinical Technique for Locating Macular Scotoma

• Macular scotoma can only be absolutely identified
  using an SLO
• Very expensive piece of equipment
• Not readily available in clinics
• Most therapists rely on a set of clinical
  observations to determine if a scotoma is present
  and its location

2
Important to Complete Macular Scotoma Assessment

• Key part of evaluation completed by OT
• Equivalent to muscle testing
• Gives a good indication of the patients
  rehabilitation potential with regards to reading
  and use of vision for occupational performance

3
Two Components are Assessed Simultaneously

• Awareness and influence of macular scotoma on
  visual performance
• Ability to compensate for macular scotoma by
  using a PRL
• Preferred retinal locus or pseudo-fovea

4
Awareness of Scotoma

• Can the patient describe blind spots when viewing
  pictures or a face?
• Each eye is tested separately

5
Ability to Locate PRL

• Instruct patient to look above, below or to the
  side of the card to see if the words/drawing
  become more complete and clear
• Experiment until a location is found that gives
  the best quality and most complete picture

6
Ability to Use the PRL to Direct Eye Movements

• Fixate on target
• Gaze shift (saccade) between targets
• Track a moving target (smooth pursuit)
• View targets at a distanceand near
• Minimize distortion (metamorphopsia)

7
Ability to Use PRL to Direct Hand in Activities
8
Assessment of Color Vision

• Changes in color vision are largely caused by
  impairment of cone function
• Always occurs to some extent with macular
  diseases
• More likely to lose blue receptors
• Optic nerve damage can also impair color vision
• More likely to lose red/green receptors
• Also occurs as a by-product of aging
• Yellowing lens restricts short wave length color

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Color Vision Assessment

• Can be tested formally
• Matching tests considered to be more accurate
  than identification tests
• Farnsworth D-15 color test
• Most often tested informally
• What colors do you see best?
• Ask patient to match paint chips of different
  colors

10
Other Visual Functionsthat Should be Assessed

• Usually assessed informally through observation
  and interview

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Adaptation to Dark/Light
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Adaptation to Dark/Light
13
Sensitivity to Glare/Light

• Three types of glare
• Discomfort
• Occurs when widely varied levels of brightness
  exist concurrently in the eyes visual field
• Disability or veiling glare
• Caused by scattering of light caused by opacities
  in the ocular media (cataract)
• Can cause a significant reduction in acuity
• Dazzling glare
• Abnormal visual sensitivity to intensity of
  ambient lighting

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Assessment of Glare Sensitivity

• Formal assessments
• Measure disability glare
• BAT (brightness acuity tester)
• Miller-Nader glare tester
• Observations
• Patient shields eyes by wearing sunglasses at all
  times or wide brimmed hat
• Patient keeps windows covered and avoids windows
  and going outdoors on sunny days
• Keeps eyes shut with light stimulus

15
Additional Assessments.

• Fluctuation of vision
• Many patients experience fluctuating vision
  through the day and from day to day
• Very common with diabetic patient

16
Phantom Vision

• Also called Charles Bonnet Syndrome or benign
  visual hallucination
• Person experiences episodes where he/she sees
  things that are not there
• Can take many forms
• Photopsia
• flashes of light, sparks, flickering, stripes,
  circles, colors
• Formed visual hallucination
• People, animals, flowers, words, etc.

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Phantom Vision cont.

• Cause is unknown
• Appears to be benign
• Doesnt signal a change in vision
• But often occurs after significant vision loss
• Research shows 53 of low vision patients
  experience episodes